Vacuum interrupter with contacts containing a minor percentage of aluminum

ABSTRACT

Discloses a vacuum-type electric circuit interrupter having its contacts formed of a porous refractory metal matrix and an alloy filling the pores of the matrix consisting essentially of copper, aluminum, and bismuth. In the alloy, the aluminum is present in a quantity of between 9 and 15 percent by weight of copperaluminum, and the bismuth is present in a quantity of less than 5 percent by weight of the total alloy.

United States Patent Horn, deceased et al.

[151 3,663,775 51 May 16,1972

VACUUM INTERRUPTER WITH CONTACTS CONTAINING A MINOR PERCENTAGE OFALUMINUM Inventors: Fordyce H. Horn, deceased, late of Schenectady, NY.by Helen W. Horn, executrix; Joseph W. Porter; Joseph L.

Talento, both of Media, Pa.

Assignee: General Electric Company Filed: Mar. 24, 1970 Appl. No.:22,250

U.S. Cl. ..200/ 144 B, 200/ l 66 C Int. Cl. ..H0lh 33/66 Field of Search..200/l44 B, 166 C [56] References Cited UNITED STATES PATENTS 2,975,2553/ I961 Lafierty ..200/ 144 B 3,497,652 2/1970 Horn et al. ..200/ 144 BPrimary ExaminerRobert S. Macon Attorney-J. Wesley l-Iaubner, WilliamFreedman, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. orman 5 7]ABSTRACT Discloses a vacuum-type electric circuit interrupter having itscontacts fonned of a porous refractory metal matrix and an alloy fillingthe pores of the matrix consisting essentially of copper, aluminum, andbismuth. In the alloy, the aluminum is present in a quantity of between9 and 15 percent by weight of copper-aluminum, and the bismuth ispresent in a quantity of less than 5 percent by weight of the totalalloy.

11 Claims, 1 Drawing Figure VACUUMINTERRUPTER WITH CONTACTS CONTAINING AMINOR PERCENTAGE OF ALUMINUM In our U.S. Pat. No. 3,497,652, there isdisclosed and claimed a vacuum-type electric circuit breaker havingcontacts formed of an alloy consisting essentially of copper, aluminum,and a weld-inhibiting metal, such as bismuth, that is substantiallyinsoluble in copper or in aluminum in the solid state. Contacts havingtheir circuitemaking and breaking regions formed entirely of such analloy have been found to provide exceptional ability to withstand a hightransient voltage immediately following a contact-separating operationthat fractures a, weld between the contacts. Such ability is of specialimportance during capacitance'switching operations inasmuchas a voltagebuilding up to twice normal peak. voltage is applied between thecontacts during the half-cycle following arc-extinction at current zero.

Contacts having their circuit-making and breaking regions formedentirely of this alloy are, however, subject to the disadvantage thattheir operational life may be too short, because of arc erosion, topermit their commercial use for highly repetitive switchingapplications.

An object of the present invention is to impart to such contactsincreased operational life without losing their exceptional ability towithstand high transient voltages immediately following contactseparation which fractures a weld.

In carrying out the invention in one form, we form the vacuuminterrupter contacts of a porous refractory metal matrix and an alloy ofcopper, aluminum, and bismuth filling the pores of the matrix, thealuminum being present in a quantity of between 9 and 15 per cent byweight of the copper-aluminum and the bismuth being present in aquantity of less than per cent by weight of the copper-aluminum-bismuthalloy, preferably about 1 percent.

Fora better understanding of the invention, reference may be had to thefollowing description taken in conjunction with the accompanyingdrawing, wherein the single FIGURE represents one embodiment of thepresent invention.

Referring now to the drawing, there is shown a vacuum-type circuitinterrupter comprising a sealed envelope l1 evacuated to a pressure of10 torr or lower. The envelopell comprises a tubular casing 12 ofinsulating material and a pair of metal end caps 13 and 14 suitablysealed to the opposite ends of casing 12. v a

Within the evacuated envelope 11 there are a pair of separabledisc-shaped contacts 17 and 18. Contact 17 is a stationary contactbrazed tothe lower end of a stationary conductive contact rod 17a; andcontact 18 is a movable contact brazed to the upper end of a verticallymovable conductive rod 18a. The movable contact rod 18a projects freelythrough an opening in the lower end cap 14, and a flexible metal bellows20 provides a suitable seal thereabout that allows vertical movement ofthe contact rod 18a without impairing the vacuum inside envelope 11.

All of theintemal parts of the interrupter are substantially free ofsurface contaminants. These clean surfaces are obtained by suitableconventional vacuum processing, which involves baking-out theinterrupter during its evacuation.

Closing of the interrupter is effected by driving the contact rod 18a inan upward'direction to drive movable contact 18 into engagement withstationary contact 17. Opening is effected by returning the movablecontact from its engaged position downwardly to its solid line positionshown. When the contacts are separated during an opening operation, anarc is drawn therebetween. Assuming an alternating current, this arepersists until a natural current zero, at which time it vanishes and isprevented from reigniting by the high dielectric strength of the vacuumin the envelope-l2. A suitable metal shield 21 of tubular form surroundsthe contact to condense the metal vapors generated by the are, thusassisting in the interrupting process. A typical gap length when thecontacts are fully open is about one-quarter inch. The opposed forwardfaces 25 of the contacts 17 and 18 may be thought of as circuit-makingand breakingregions of the contacts.

When the contacts are driven into engagement during closing, they maybounce apart slightly and draw an arc between their circuit-making andbreaking regions 25 before being driven back into engagement. T hisarctends to produce welding together of the contacts when they reengageunder pressure. The contacts of a vacuum interrupter have a greatertendency toward such welding than those of other type interruptersbecause their surfaces are exceptionally clean and free ofweld-inhibiting films.

One of the problems that the present invention is concerned with. isproviding an, interrupter that can withstand high transient voltagesimmediately following a contact-separating operation that fractures aweld between the contacts. In the aforesaid U.S. Pat. No. 3,497,652, wedisclose and claim a vacuum interrupter that has its contacts formed ofan alloy of copper, aluminum and a weld-inhibiting metal, such asbismuth, that is substantially insoluble in copper and aluminum in thesolid state and is distributed throughout the copper-aluminum. Thealuminum is present in this alloy in a quantity of 9 to 15 percent byweight of the copper-aluminum and the bismuth in a quantity of below 5percent. This alloy has shown exceptional ability to'meet theabove-described voltage-withstand requirement.

Contacts having their circuit-making and breaking regions formedentirely of this alloy are, however, subject to the disadvantage thattheir operational life may be too short, because of arc-erosion, topermit their commercial use for highly repetitive switchingapplications.We overcome this disadvantage, and, in particular, do so without losingthe exceptional ability .of the contacts to withstand a high transientvoltage after weld-fracture by constructing the contacts 17 and 18 of aporous refractory metal matrix having its pores filled with theaforesaid alloy. As a specific example, we constructthe contacts of arefractory metal matrix of tungsten having its pores filled with analloy of copper-aluminum-bismuth, with the aluminum present in aquantity of 12 percent by weight of the copper-aluminum and the bismuthin a quantity of 1 percent by weight of the copper-aluminum-bismuthalloy. For the reasons explained in our aforesaid U.S. Pat. No.3,497,652, the aluminum content of this alloy should be between about 9and 15 percent by weight of the copper-aluminum. The bismuth contentshould be less than 5 percent by weight of the alloy and, preferably, aslow as possible, consistent with the need to reduce contact-welding toan acceptable level. The bismuth is distributed throughout thecopper-aluminum.

These contacts are made by employing the following steps in the sequencestated: (1) pressing tungsten powder in air to about 60 percent density;(2) sintering the pressed tungsten powder in hydrogen at a temperatureof 2,300 F.;' (3) im- 'pregnating the resultant structure in hydrogenwith the copper-aluminum-bismuth alloy at about the same temperature;(4) cooling the composite in hydrogen to solidify the alloy; (5)reheating the composite in an inert gas such as argon to a sufficienttemperature to remelt the alloy and for a sufficient period toaccomplish degassing of the composite structure; (6) allowing thecomposite to cool in the argon atmosphere; and (7) machining ofi' theexcess material and machining to size. The alloy is substantially freedof gas before it is used to impregnate the tungsten. The degassing step,in driving off the hydrogen from the composite, leaves the compositesubstantially free of absorbed gas.

Although tungsten is preferred for the refractory metal, otherrefractory metals are also suitable for this-purpose, e.g.,

, molybdenum, tungsten carbide, and molybdenum carbide.

aluminum. The tertiary metal is present in each of these alloys in lessthan 5 per cent by weight of the total alloy for weld-inhibitingpurposes and is distributed throughout the alloy. The firstmentioned ormajor constituent of each alloy is referred to as the primary metal.

The weld-inhibiting agent in each of the alloys discussed hereinabovehas a lower freezing temperature than the primary metal-aluminum alloy,is substantially insoluble in the other constituents of the alloy in thesolid state, and is distributed throughout the alloy. In referring toweld-inhibiting agents that are substantially insoluble in the otherconstituents in the solid state, we are referring to weld-inhibitingmetals that have a solid state solubility in the other constituents ofless than about 2 percent by weight of the alloy considered at theeutectic temperature of said alloy or the freezing temperature of theweld-inhibiting constituent if there is no eutectic.

In those applications where a moderate amount of weld strength can betolerated, the weld-inhibiting metal can be entirely, or almostentirely, eliminated from the final contact material. This can be doneby performing the aforementioned manufacturing steps (5) and (6), i.e.,the reheating and cooling steps, in a vacuum instead of in the argonatmosphere. The reheating in vacuum evaporates substantially all of thelowmelting-point weld-inhibiting metal, e.g., bismuth, leaving thecontact substantially free of the weld-inhibiting metal.

While we have shown and described particular embodiments of ourinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from ourinvention in its broader aspects;

and we, therefore, intend herein to cover all such changes andmodifications as fall within the true spirit and scope of our invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A vacuum-type electric circuit interrupter comprising:

a. an envelope evacuated to a pressure of 10" mm. of mercury or less,

b. a pair of contacts within said envelope relatively movable into andout of engagement,

c. said contacts being substantially free of absorbed gases and surfacecontaminants, at least one of said contacts having its circuit-makingand breaking regions formed of a porous refractory metal matrix and analloy filling the pores of said matrix consisting essentially ofcopper-aluminum and bismuth,

the aluminum being present in a quantity of between 9 and 15 percent byweight of the copper-aluminum, and the bismuth being present in aquantity of less than about 5 percent by weight of the total alloy andin a sufficient quantity to inhibit contact-welding, and beingdistributed throughout said alloy.

2. The vacuum-type circuit interrupter of claim 1 in which the aluminumis present in a quantity of between 11 and 13 percent by weight of thecopper-aluminum.

3. The vacuum-type circuit interrupter of claim 1 in which the aluminumis present in a quantity of about 12 percent by weight of the copperaluminum.

4. The vacuum type circuit interrupter of claim 1 in which saidrefractory metal is tungsten.

5. A vacuum-type electric circuit interrupter comprising:

a. an envelope evacuated to a pressure of 10 mm. of mercury or less,

b. a pair of contacts within said envelope relatively movable into andout of engagement,

0. said contacts being substantially free of absorbed gases and surfacecontaminants,

d. at least one of said contacts having circuit-making and breakingregions formed of a porous refractory metal matrix and an alloy fillingthe pores of said matrix consisting essentially of copper-aluminum and aweld-inhibiting metal having substantially no solid-state solubility incopper or aluminum and having an effective freezing temperature belowthat of copper-aluminum,

e. the aluminum being present in a quantity of between 9 and 15 percentby weight of the copper-aluminum, and

f. the weld-inhibiting metal being present in a quantity of less thanabout 5 percent by weight of the total alloy and in a quantitysufficient to inhibit contact-welding, and being distributed throughoutsaid alloy.

6. A vacuum-type electric circuit interrupter comprising:

a. an envelope evacuated to a pressure of 10 mm. of mercury or less,

b. a pair of contacts within said envelope relatively movable into andout of engagement,

0. contacts being substantially free of absorbed gases and surfacecontaminants,

d. at least one of said contacts have circuit-making and breakingregions formed of a porous refractory metal matrix and an alloy fillingthe pores of said matrix consisting essentially ofcopper-aluminum-bismuth, or silver-aluminum-bismuth, ornickel-aluminum-bismuth,

e. the aluminum being present in a quantity of: between 9 and 15 percentby weight of the copper-aluminum in the case of copper-aluminum-bismuth,between 5 and 10 percent by weight of the silver-aluminum in the case ofsilver-aluminum-bismuth, and between 8 and 13 percent by weight of thenickel-aluminum in the case of nickelaluminum-bismuth,

f. the bismuth being present in a quantity of less than about 5 percentby weight of the total alloy and in a quantity sufficient to inhibitcontact-welding, and being distributed throughout said alloy.

. A vacuum-type electric circuit interrupter comprising:

a. an envelope evacuated to a pressure of 10 mm. of mercury or less,

b. a pair of contacts within said envelope relatively movable into andout of engagement,

c. said contacts being substantially free of absorbed gases and surfacecontaminants,

d. at least one of said contacts having its circuit-making and breakingregions formed of a refractory metal matrix and an alloy filling thepores of said matrix consisting'essentially of: (l) copper-aluminumcontaining 9 to 15 percent by weight of aluminum, or (2) silver-aluminumcontaining 5 to 10 percent by weight of aluminum, or (3) nickelaluminumcontaining 8 to 13 percent by weight of aluminum, and a weld-inhibitingmetal,

' e. said weld-inhibiting metal having substantially no solidstatesolubility in the primary metal of the alloy or aluminum and having aneffective freezing temperature below that of the primary metal-aluminumalloy,

f. said weld-inhibiting metal being present in a quantity less thanabout 5 percent by weight of the total alloy and in a quantitysufficient to inhibit contact welding, and being distributed throughoutsaid total alloy.

8. A vacuum-type electric circuit interrupter comprising:

a. an envelope evacuated to a pressure of 10 mm. of mercury or less,

b. a pair of contacts within said envelope relatively movable into andout of engagement,

0. said contacts being substantially free of absorbed gases and surfacecontaminants,

d. at least one of said contacts having its circuit-making and breakingregions formed of a porous refractory metal matrix and an alloy fillingthe pores of said matrix consisting essentially of l) copper-aluminumcontaining 9 to 15 percent by weight of aluminum, or (2) silver-aluminumcontaining 5 to 10 percent by weight of aluminum, or (3) nickel-aluminumcontaining 8 to 13 percent by weight of aluminum.

9. The vacuum-type circuit interrupter of claim 8 in which said alloyconsists essentially of copper-aluminum.

10. The vacuum-type circuit interrupter of claim 8 in which said alloyconsists essentially of silver-aluminum.

l l. The vacuum-type circuit interrupter of claim 8 in which said alloyconsists essentially of nickel-aluminum.

2. The vacuum-type circuit interrupter of claim 1 in which the aluminumis present in a quantity of between 11 and 13 percent by weight of thecopper-aluminum.
 3. The vacuum-type circuit interrupter of claim 1 inwhich the aluminum is present in a quantity of about 12 percent byweight of the copper aluminum.
 4. The vacuum type circuit interrupter ofclaim 1 in which said refractory metal is tungsten.
 5. A vacuum-typeelectric circuit interrupter comprising: a. an envelope evacuated to apressure of 10 4 mm. of mercury or less, b. a pair of contacts withinsaid envelope relatively movable into and out of engagement, c. saidcontacts being substantially free of absorbed gases and surfacecontaminants, d. at least one of said contacts having circuit-making andbreaking regions formed of a porous refractory metal matrix and an alloyfilling the pores of said matrix consisting essentially ofcopper-aluminum and a weld-inhibiting metal having substantially nosolid-state solubility in copper or aluminum and having an effectivefreezing temperature below that of copper-aluminum, e. the aluminumbeing present in a quantity of between 9 and 15 percent by weight of thecopper-aluminum, and f. the weld-inhibiting metal being present in aquantity of less than about 5 percent by weight of the total alloy andin a quantity sufficient to inhibit contact-welding, and beingdistributed throughout said alloy.
 6. A vacuum-type electric circuitinterrupter comprising: a. an envelope evacuated to a pressure of 10 4mm. of mercury or less, b. a pair of contacts within said enveloperelatively movable into and out of engagement, c. contacts beingsubstantially free of absorbed gases and surface contaminants, d. atleast one of said contacts have circuit-making and breaking regionsformed of a porous refractory metal matrix and an alloy filling thepores of said matrix consisting essentially of copper-aluminum-bismuth,or silver-aluminum-bismuth, or nickel-aluminum-bismuth, e. the aluminumbeing present in a quantity of: between 9 and 15 percent by weight ofthe copper-aluminum in the case of copper-aluminum-bismuth, between 5and 10 percent by weight of the silver-aluminum in the case ofsilver-aluminum-bismuth, and between 8 and 13 percent by weight of thenickel-aluminum in the case of nickel-aluminum-bismuth, f. the bismuthbeing present in a quantity of less than about 5 percent by weight ofthe total alloy and in a quantity sufficient to inhibit contact-welding,and being distributed throughout said alloy.
 7. A vacuum-type electriccircuit interrupter comprising: a. an envelope evacuated to a pressureof 10 4 mm. of mercury or less, b. a pair of contacts within saidenvelope relatively movable into and out of engagement, c. said contactsbeing substantially free of absorbed gases and surface contaminants, d.at least one of said contacts having its circuit-making and breakingregions formed of a refractory metal matrix and an alloy filling thepores of said matrix consisting essentially of: (1) copper-aluminumcontaining 9 to 15 percent by weight of aluminum, or (2) silver-aluminumcontaining 5 to 10 percent by weight of aluminum, or (3) nickel-aluminumcontaining 8 to 13 percent by weight of aluminum, and a weld-inhibitingmetal, e. said weld-inhibiting metal having substantially no solid-statesolubility in the primary metal of the alloy or aluminum and having aneffective freezing temperature below that of the primary metal-aluminumalloy, f. said weld-inhibiting metal being present in a quantity lessthan about 5 percent by weight of the total alloy and in a quantitysufficient to inhibit contact welding, and being distributed throughoutsaid total alloy.
 8. A vacuum-type electric circuit interruptercomprising: a. an envelope evacuated to a pressure of 10 4 mm. ofmercury or less, b. a pair of contacts within said envelope relativelymovable into and out of engagement, c. said contacts being substantiallyfree of absorbed gases and surface contaminants, d. at least one of saidcontacts having its circuit-making and breaking regions formed of aporous refractory metal matrix and an alloy filling the pores of saidmatrix consisting essentially of (1) copper-aluminum containing 9 to 15percent by weight of aluminum, or (2) silver-aluminum containing 5 to 10percent by weight of aluminum, or (3) nickel-aluminum containing 8 to 13percent by weight of aluminum.
 9. The vacuum-type circuit interrupter ofclaim 8 in which said alloy consists essentially of copper-aluminum. 10.The vacuum-type circuit interrupter of claim 8 in which said alloyconsists essentially of silver-aluminum.
 11. The vacuum-type circuitinterrupter of claim 8 in which said alloy consists essentially ofnickel-aluminum.